No one who has seen a baby sinking back satiated from the breast and falling asleep with flushed cheeks and a blissful smile can escape the reflection that this picture persists as a prototype of the expression of sexual satisfaction in later life.
Sigmund Freud (1856–1939), Austrian psychiatrist. repr. in Complete Works, vol. 7, eds. James Strachey and Anna Freud (1953). "Infantile Sexuality," sct. 2, Three Essays on the Theory of Sexuality (1905).